Hybrid vehicles may be required to meet emissions regulations for hydrocarbons, carbon monoxide, and oxides of nitrogen. One way to meet emissions regulations is to couple a three-way catalyst to an engine of the hybrid vehicle so that engine emissions are oxidized and reduced to more desirable gases. However, even with a three-way catalyst, a hybrid vehicle may not meet emissions regulations because the three-way catalyst may have to reach a light-off temperature (e.g., a temperature where catalyst efficiency reaches a threshold efficiency) before engine exhaust gases may be processed. One way to shorten an amount of time a catalyst takes to reach light-off temperature is to retard engine spark timing away from minimum spark advance for best torque (MBT). By retarding spark timing, exhaust gases may transfer additional heat to the engine's exhaust system and its components. Nevertheless, retarding engine spark timing may be insufficient to heat a catalyst to a light off temperature soon enough to meet emissions regulations. Therefore, it would be desirable to provide a way to reach catalyst light off temperature sooner.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method, comprising: operating an engine with a substantially constant air mass and spark timing in response to catalyst temperature less than a threshold; varying engine torque as engine speed varies while operating the engine with the substantially constant air mass; and providing driver demand torque via engine torque and motor torque while operating the engine with the substantially constant air mass.
By operating an engine with a substantially constant air mass flowing through the engine, substantially constant spark retard, and varying engine torque as engine speed varies, it may be possible to provide the technical result of quickly heating a catalyst while producing a desired driver demand torque. In particular, the engine air mass may be selected to provide a desired rate of thermal energy from the engine to a catalyst so that the catalyst lights off within a desired time even in the presence of varying vehicle speed and driver demand torque. A motor coupled to the engine may augment or lower engine torque to provide a driver demand torque at a torque converter impeller as engine speed changes during vehicle acceleration and deceleration. In this way, flow of air through an engine may be held substantially constant even as engine speed changes so that a catalyst lights off in a repeatable fashion as a vehicle accelerates or decelerates.
The present description may provide several advantages. In particular, the approach may improve vehicle emissions. Further, the approach may improve vehicle drivability during engine starting. Additionally, the approach may allow more accurate air-fuel ratio control while engine emissions components are being heated to operating temperature.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.